Inboard Diesel
June 13, 2009 by Chris Wethered
Filed under Boat Engines And Sailboat Hardware
In order to calculate the horsepower required for inboard diesels,
First you need to calculate the following:
- Boat size
- Displacement
Your sailboat manufacture will be able to supply this data, should you not have it handy.
How to calculate hull speed
To achieve theoretical max boat speed your engine should be at half of it's available power range. That's 3/4 of the RPM on the counter.
Theoretical maximum
Work out the theoretical hull speed in calm water. Plus the horsepower required to do this. Manufactures have figures for this as well. The idea is to use medium revs rather than exerts the engine. You should never have to use maximum revs - if you do then you'll burn it out more quickly.
Solving the under power issue
Simply putting a higher horsepower engine in won't solve the problem either
- The weight of the engine may put the boat out of balance
- The extra power will be predominately useless too
- This is because your hull and boat overall is not designed for the increase
- Don't shake your boat to bits!
Another consideration is the propeller.
It's all about efficiency through patient mantainence
Here is a list of things to bare in mind:
- The number of blades on your present propeller
- The current pitch of them
- The material used in manufacture
- The condition
The difference for example between three blades and four is considerable.
Check with your engine manual, find out what the engine should be doing when new. Use your judgment and determine if changing either the propeller or engine is going to impact your boat speed.
Take advantage! West Marine are offering a 10% discount, when you spend over $100!
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